[Bug binutils/27206] .symver overrides .weak

[tkacvins at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27206

--- Comment #6 from Tom Kacvinsky <tkacvins at gmail dot com> ---
For compatibility reasons, I want to update my automated build machine, but
build GCC and auxiliary support libraries in such a fashion that we can target
older Linux distributions That is, build on a machine with a newer glibc, but
still be able to run the resulting binaries on a system with an older glibc,
which is reverse of building on an older system and running on a newer system.

So, I first went to build GCC 8.3.0 on a newer system (CentOS 7) using a custom
assembly file (one that contains a .symver for each older version symbol we
want, to target older versions of glibc).  That is injected into compiler
generated assembly files via an indirect assembler - named as, which opens any
.s/.S files on the command line, inserts the custom assembly file into them,
then calls gas, the _real_ assembler.

But libgcc.so.1 failed to build with the pthread_key_create error I mentioned
in this bug.  The reproducer I sent is a stripped down version of the code from
libgcc.

This is why I am somewhat concerned about the link map trick, etc...  It would
create many problems while trying to sort out the GCC build configuration and
code.  The code in GCC that utilizes pthread_key_create marks it as extern and
weak, which is different from what is in pthread.h.  And the reason for that,
as commented in the libgcc code, is so that pthread_key_create is weak, which
leads libggc.so.1 not having a run time dependency on libpthread.so.0.


Tom

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